The effect of deleting the genes encoding the twin-arginine translocation (Tat)system on H2 production by Escherichia coli strain MC4100 and its formate hydrogenlyase upregulated mutant (DhycA) was investigated. H2 evolution tests using two mutant strains defective in Tat transport (DtatC and DtatA-E) showed that the rate doubled from 0.88\(\pm)\0.28mL H2 mg dry weight�1 L culture�1 in the
parental strain, to 1.70�0.15 and 1.75�0.18mL H2 mg dry weight�1 L culture�1,respectively, in the DtatC and DtatA-E strains. This increase was comparable to that of a previously characterized hydrogen over-producing E. coli strain carrying a DhycA allele. Construction of a tatC, DhycA double deletion strain did not increase hydrogen production further. Inactivation of the Tat system prevents correct assembly of the uptake hydrogenases and formate dehydrogenases in the cytoplasmic membrane and it is postulated that the subsequent loss of basal levels of
respiratory-linked hydrogen and formate oxidation accounts for the observed increases in formate-dependent hydrogen evolution.